Method for making glass fiber reinforced thermoplastic polymer articles



United States Patent 3,396,142 METHOD FOR MAKING GLASS FIBER RE-INFORCED THERMOPLASTIC POLYMER ARTICLES Arthur George Little, Auburn,and Allan D. Martin, Sanford, MiclL, assignors to The Dow ChemicalCompany,

Midland, Mich, a corporation of Delaware No Drawing. Filed Apr. 24,1963, Ser. No. 275,223

6 Claims. ((11. 26041) This invention relates to the preparation ofglass fiber reinforced thermoplastic polymer articles. It pertainsespecially to an improved process for making shaped articles of glassfiber reinforced thermoplastic polymers by an injection moldingtechnique.

It is known to prepare laminates and compositions containing glass fiberreinforcing material embedded in or laminated with a resinous material.

In preparing fiberglass reinforced thermoplastic polymer articles byinjection molding it is common practice to compound the heat-plastifiedpolymer with the glass fiber to intimately mix and coat or encase theglass fibers in the plastic polymer. The product containing theencapsulated glass fibers or chopped strands, uniformly or substantiallyuniformly distributed throughout, is cooled and ground or cut to agranular form suitable for molding, and can readily be shaped byinjection molding techniques to form articles of uniform and a desiredquality.

We have now discovered that uniform desirable glass fiber reinforcedthermoplastic polymer articles can readily be prepared by injectionmolding operations by blending together a normally solid thermoplasticpolymer in the form of particles of sizes not greater than about 12 meshper inch as determined by US. Standard screens and a reinforcing amountof chopped strand glass fibers of lengths between about and W inch,preferably chopped strand glass fibers of about inch length, inproportions of from about 60 to 95 percent by weight of thethermoplastic polymer and correspondingly from about 40 to percent byweight of the chopped strand glass fibers, to obtain a uniform orsubstantially uniform dry mixture of the materials and thereafterfeeding, or using the mixture as the feed, in an injection moldingprocess, advantageously to a standard extruding injection moldingmachine, and making shaped articles of the fiberglass reinforcedthermoplastic polymer by the injection molding process.

Thermoplastic ploymers that can be employed in the process are thenormally solid homopolymers and c0- polymers of one or more monovinylaromatic compounds having the general formula wherein Ar is an aromatichydrocarbon or a halohydrocarbon of the benzene series such as styrene,vinyltoluene, vinylxylene, chlorostyrene, dichlorostyrene, bromostyreneor copolymers of at least 50 percent by weight of one or more of sucharomatic compounds and a minor proportion of another monoethylenicallyunsaturated organic compound copolymerizable therewith such as methylmethacrylate, acrylonitrile or alpha-methyl styrene, or polyolefins suchas polyethylene, polypropylene, or ethylcellulose, poly(methylmethacrylate), or copolymers of a major proportion by weight of methylmethacrylate and a minor amount of a monovinyl aromatic compound, egstyrene.

It is important that the polymer be in powdered or granular form, i.e.in particles of sizes not appreciably greater than 12 mesh per inch asdetermined by US. Standard screens. In a preferred embodiment thethermoplastic polymer is in the form of particles of a mixture of sizesnot greater than about 16 mesh, for example, 5

3,396,142 Patented Aug. 6, 1968 percent on a No. 16 mesh screen, about70 percent on a No. 40 mesh screen and about 25 percent through a No. 40mesh screen, or as fines.

Small amounts of additives such as antioxidants, pigments, dyes, colors,heat stabilizing agents, light stabilizing agents, flow agents,plasticizers, mold release agents and the like may also be incorporatedwith the polymer or with the dry blend of the polymer and the choppedstrand fiberglass material, but such additives are not required in theinvention. The additives, when used, are usually employed in amountscorresponding to form about 0.5 to 5 percent by weight of the polymer.

The following examples illustrate ways in which the principles of theinvention has been applied, but are not to be construed as limiting itsscope.

Example 1 A charge of 700 grams of a resinous copolymer of approximately27 percent by weight acrylonitrile and 73 percent styrene, in the formof particles of sizes as determined by US. Standard screens as follows:through a No. 12 screen, on a N0. 25 screen, 70 percent; through a N0.25 screen, on a No. 40 screen, 20 percent; through a N0. 40 screen, 10percent by weight, and having blended therewith 0.051 percent by weightof Nopcowax and 0.083 percent by weight of polyethylene glycol having anaverage molecular weight of 200, was placed in a one gallon wide mouthjar, together with 300 grams of chopped strand At-inch long fiberglass.The mixture was blended by tumbling the same for a period of fiveminutes. Portions of the blended mixture were injection molded in a oneounce Watson Stillman Injection Molding Machine to form test pieces of/2 x /8 inch cross section. The molded test pieces had the fiberglassuniformly distributed throughout and had the properties:

In each of a series of experiments, a copolymer of styrene andacrylonitrile in proportions similar to that of the copolymer used inExample 1, except that the copolymer was in the form of particles ofsizes as determined by U.S. Standard screens as follows: on a N0. 12screen 0.2 percent; on a No. 25 screen 69.7 percent; on a No. 40 screen20.1 percent; on a No. '80 screen 9.5 percent; fines 0.5 percent, wasplaced in a wide mouth glass jar and blended with it-inch long choppedstrand fiberglass in proportions as hereinafter stated by tumbling inthe glass jar for a period of five minutes. Portions of the blendedmaterial were injection molded to form test bars. The compositions andthe properties of the molded product were as follows:

Fiberglass, Molding Room Tensile Notched impercent temp, F. pressure,strength, pact strength,

lbs/sq. in. lbs/sq. in. ft.-lbs.

In each of a series of experiments, a copolymer of styrene andacrylonitrile in proportions similar to that of the cop'olymer used inExample 1, except that the copolymer was in the'form of particles ofsizesas determined by U.S. Standard screens as followsk'on :a No. 12screen 0.2 percent; on a No. 25 screen 0.8 percent; on a No. 40 screen30.2 percent; on a No. 80 'screen'49.3 percent; fines 19.5 percent. The'copolymer was blended with flt-inch long chopped strand fiberglass bytumbling, was injection molded and was tested employing proceduresimilar to those employed in the preceding examples. The compositionsand the properties of the molded product were as follows: a Y

Fiberglass, Molding Room Tensile Notched impercent temp, F. pressure,strength, pact strength,

lbs/sq. in. lbs/sq. in. ft.-lbs.

Example 4 Polymer Fiber- Tensile Impact glass, strength, strength, KindPercent Percent lbs/sq. in. ft.-1bs.

We claim:

1. In a process for making shaped articles from a composition comprisinga major proportion by weight of a normally solid thermoplastic polymerand a minor amount of glass fibers, the improvement which consists inblending together from 60 to 95 parts by weight of a normally solidthermoplastic organic polymer in the form of particles of sizes notsubstantially greater than 12 mesh per inch as determined by U.S.Standard screens and from 40 to 5 percent by weight of chopped strandfiber glass in lengths between and 7 inch, and thereafter mold- [:4 r .1ing said mixture of materials into shaped articles by injection moldingtechniques. r

2. In a process for making shaped articles from a composition comprisinga major proportion by weight of a normally solid thermoplastic polymerand a minor amount of glass fibers, the improvement which consists inblending together from to '95 parts by weight E solid thermoplasticorganic polyme'rinthe ticles of sizes not substantially greater th aril2 inch as determined by U.S.;Standa'rd screensf to 5 parts by weight'ofchopped strand fibe fjgl ss. m lengths between and. inch, andthereafter-knowing said mixture of materials into shaped articles by anextruding injection molding technique.

3. A process for making shaped'articles of fiberglass reinforcedthermoplastic polymers, which. process come prises blending togetherfrom 60 to 95 parts by weight of a normally solid thermoplastic organicpolymer in the form of particles of sizes not greater than 12 mesh perinch and consisting of about 95 percent of saidpolymer in the form ofparticles of sizes smaller than 16 mesh per inch as determined by U.S.Standard screens and from 40 to 5 percent by weight of. chopped strandglass fibers in lengths between andF/ inch, and there-after molding saidmixture materials into shaped articles by anextruding injection moldingtechnique. 1

4. A process as claimed in claim 3 wherein thethermoplastic polymer ispolystyrene. i

5. A process as claimed in claim 3 wherein the chopped strand glassfibers are in lengths of approximately /It-inch.

6. A process as claimed inclaim 3 wherein'approximately parts by weightof polystyrene is blended with approximately 30 parts by weight ofchopped strand glass fibers.

References Cited UNITED STATES PATENTS 7 2,721,357 10/1955 Hochberg2604l X 2,936,487 5/1960 Paz 2604l 3,072,581 1/1963 Platzer 260 4lUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,396,142 August 6, 1968 Arthur George Little et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

line 36, in the heading of the third vertical "Room" should read Ramline 59, in

d vertical column in Example 2, "Room" Column 2, column in Example 1,the heading of the thir should read Ram Column 3, line 12, in theheading of the third vertical column in Example 3, "Room" should readRam Signed and sealed this 6th day of January 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. IN A PROCESS FOR MAKING SHAPED ARTICLES FROM A COMPOSITION COMPRISINGA MAJOR KPROPORTION BY WEIGHT OF A NORMALLY SOLID THERMOPLASTIC JPOLYMERAND A MINOR AMOUNT OF GLASS FIBERS, THE IMPROVEMENT WHICH CONSISTS INBLENDING TOGETHER FROM 60 TO 95 PARTS BY WEIGHT OF A NORMALLY SOLIDTHERMOPLASTIC ORGANIC POLYMER IN THE FORM OF PARTICLES OF SIZES NOTSUBSTANTIALLY GREATER THAN 12 MESH PER INCH AS DETERMINED BY U.S.STANDARD SCREENS AND FROM 40 TO 5 PERCENT BY WEIGHT OF CHOPPED STRANDFIBER GLASS IN LENGTHS BETWEEN 3/16 AND 9/16 INCH, AND THEREAFTERMOLDING SAID MIXTURE OF MATERIALS INTO SHAPED ARTICLES BY INJECTIONMOLDING TECHNIQUES.